In production of semiconductors, liquid crystal panels or the like, high-speed transfer and highly cleaned atmospheres for the substrates, such as wafers, glass plates or the like, have been required more and more. For instance, in the field of producing the semiconductors, an effective means for taking out the wafers from a cassette and then carrying them into a suitable container (or another cassette) for receiving them therein at a relatively high speed has been demanded.
In some cases, upon carrying the wafers to and from an apparatus for providing a certain process to the wafers, a hand (or end effector) of the robot used for carrying each wafer (or wafers) into the apparatus before the wafer is subjected to the process should be changed with another hand for taking out the wafer from the apparatus after the wafer is subjected to the process.
For instance, in the case of the robot employed in the apparatus for cleaning the wafers, the hand for handling unclean wafers (i.e., the wafers before cleaned) should be securely changed with the hand for handling clean wafers (i.e., the wafers after cleaned), or vice versa. Further, in the case of the robot for carrying the wafers to and from the apparatus for processing the wafers under a high temperature condition, the hand for handling the wafers under the high temperature condition should be changed with the hand for handling the wafers in a normal temperature state, or vice versa.
Usually, two hands are provided to the robot for carrying and/or handling the wafers as described above. In this case, each hand is exclusively used for each purpose as described above. Therefore, the operation of such two hands may tend to require so much time and skill, making it rather difficult to substantially enhance the throughput.
Employment of a large number of robots, each having such two hands as described above, could actually enhance the throughput of the wafer transfer. However, this approach should rather increase the cost required for the equipment, thus canceling the effect of reducing the cost that could be obtained by such enhancement of the throughput. Furthermore, the fact that two robots cannot access one wafer cassette at a time also makes it difficult to enhance the throughput.
To address such problems, one approach can be mentioned, in which a plurality of hands are fixedly provided to one robot arm, while being vertically shifted in position along the robot arm, with an interval between the hands corresponding to a pitch of the wafers to be respectively stored and arranged in the cassette. With this approach, the wafers can be carried, collectively at a time, to and from the wafer cassette. For instance, if two hands are provided to the one robot arm, while being vertically shifted along the robot arm with the interval between the hands corresponding to the pitch of the wafers, two wafers can be actually carried at a time.
However, in such a case in which the plurality of hands are fixedly provided to the one robot arm while being vertically shifted in position along the robot arm, depending on the position of slots in the wafer cassette, the other hand holding no wafer may interfere with the cassette and/or wafers already inserted in the cassette upon insertion of the wafer into the cassette, so that the wafer held on the hand can no longer be inserted in the cassette.
For instance, upon insertion of the wafers into the wafer cassette capable of storing therein twenty five (25) sheets of wafers by using the robot having two hands provided to the one robot arm thereof, two wafers, respectively taken out for each operation by the two hands from the container or cassette located on the take-out side, are carried in succession into the wafer cassette located on the take-in side. However, upon the insertion of the last one wafer finally left in the container or cassette located on the take-out side, the one hand holding no wafer may tend to interfere with the wafers already inserted in the cassette and/or cassette itself. Therefore, this robot cannot securely carry such a twenty-fifth wafer.
Further, in the case of carrying one wafer from any given slot (e.g., a first slot) of one cassette located on the take-out side into the same slot (i.e., the first slot) or different slot (e.g., a third slot) of another cassette located on the take-in (or wafer receiving) side, a similar interferential problem may tend to occur between the hands and the wafers already carried in the cassette.
Namely, in such a robot having the plurality of hands, which are fixedly provided to the one robot arm while being vertically shifted in position along the robot arm, there still remain many restrictions and problems that may rather deteriorate flexibility in the operation of the robot.